This invention is directed in general to mechanisms for tracking moving webs, and more particularly to a simplified web tracking mechanism which provides for automatic control of lateral movement of a web.
Electrostatographic reproduction apparatus employ a sensitized member upon which an image of information to be reproduced is formed. The sensitized member is typically a drum or continuous web of material adapted to move so as to present an area of the member successively to electrostatographic process stations. For certain reproduction apparatus, the continuous web sensitized member has certain advantages over the drum in that it is generally less expensive and easier to replace at the end of its functional life or when inadvertently damaged.
The sensitized member of the continuous web type is typically supported by, and driven about, a plurality of rollers which serve to define a desired travel path relative to the electrostatographic process stations. Manufacturing tolerances associated with making of a continuous web results in a degree of conicity in the continuous web. Also, due to the inability to manufacture perfectly cylindrical rollers or exactly mount the rollers in a web supporting system, the velocity vector of a traveling web frequently approaches the longitudinal axis of a support roller at an angle other than substantially normal to such axis. As a result of the conicity of the continuous web and the angular deviation of the web velocity vector from normal with respect to the support roller axis, a moving web has the undesirable tendency to move laterally with respect to its desired travel path. If not controlled, such lateral movement results in mis-alignment of the web with the electrostatographic process stations thereby causing failure of the reproduction apparatus to make copies of acceptable quality. Ultimately, it can lead to destruction of the web.
Various mechanisms for correcting for lateral (cross-track) movement of a web have heretofore been utilized. Such mechanisms include for example servo actuated steering rollers (such as shown for example in U.S. Pat. No. 4,572,417, issued Feb. 25, 1986, in the name of Joseph et al.) and self-activated steering rollers (such as shown for example in U.S. Pat. No. 4,397,538, issued Aug. 9, 1983, in the name of Castelli et al.). In order to compensate for web conicity and angular deviation of the web velocity vector, such mechanisms are generally of a complex construction and high cost.